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Earth's deepest earthquake swarms track fluid ascent beneath nascent arc volcanoes.

White, Lloyd T. and Rawlinson, Nicholas and Lister, Gordon S. and Waldhauser, Felix and Hejrani, Babak and Thompson, David A. and Tanner, Dominique and Macpherson, Colin G. and Tkalčić, Hrvoje and Morgan, Jason P. (2019) 'Earth's deepest earthquake swarms track fluid ascent beneath nascent arc volcanoes.', Earth and planetary science letters., 521 . pp. 25-36.

Abstract

Most of the world's explosive volcanoes are located in volcanic arcs, formed by fluid-fluxed melting of upper mantle rocks. The fluids that facilitate melting are released from subducted tectonic plates as they sink into the mantle. Yet, we have sparse knowledge of the migration pathways of melts through the upper mantle (i.e., between the surface of the subducted plate and arc volcanoes). We are also uncertain of the time required for this migration to occur. Here, we show evidence of two earthquake swarms that occur in the upper mantle beneath the Mariana and Izu-Bonin arc systems. The best-resolved swarm occurs beneath the Mariana arc, where the earthquakes define a sub-vertical pipe-like structure with a diameter of ∼50 km and occurs between depths of ∼10–250 km. To test the robustness of depth locations, we used a fully non-linear grid search algorithm, double-difference relocation, as well as an analysis of pP-P arrival times and depth sensitive phases. In addition, we calculated centroid moment tensor solutions using a 3D Earth model to understand the mechanism of failure within the swarms. These data demonstrate that the sub-vertical earthquake swarm occurs within the upper mantle between the subducted slab and the overriding volcanic arc, with seismicity concentrated within discrete day- to month-long swarms of activity over a single two-year period. The Izu-Bonin example shares a similar sub-vertical pipe-like geometry with seismic activity bracketed within a two-year period. We infer that these rare earthquake swarms record the ascent of hydrous melt and/or fluid, from dehydration of the subducting plate. This implies that hydrous minerals within subducted slabs continue to dehydrate to depths of at least 200–250 km. Also, the short duration of earthquake swarms implies that fluids/melts can be rapidly transported through the sub-arc mantle at rates in the order of km/hr. This is consistent with rapid melt ascent rates inferred from geospeedometry and experimental petrology and is reminiscent of patterns seen during episodic tremor and slip events.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.epsl.2019.05.048
Publisher statement:© 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license. (http://creativecommons.org/licenses/by/4.0/)
Date accepted:31 May 2019
Date deposited:18 June 2019
Date of first online publication:17 June 2019
Date first made open access:18 June 2019

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